Ice and frost formation on windows creates severe limitations in peoples' daily lives. Such formation on building windows limits and sometimes blocks visibility through the windows, which may be critical in the cases of observation points and military lookout posts. The problem of ice and frost formation has a severe effect on safety when it appears on windows and mirrors of vehicles such as cars, truck, boats, airplanes, etc.
There is a clear need to prevent the formation of ice and frost on surfaces, and especially on windows at specific times and there is a need to enable the removal of ice and frost in such cases that the formation of ice and frost was not prevented, when ice and frost free surfaces are required.
Since the first time people started using windows, devices, systems and methods began to develop in order to address the problem of ice and frost formation. These are based among other things on mechanical removal of the ice and frost by means of wipers, brushes or other tools, by mechanical removal using air flow, heating by means of electrical conductors glued to the windows and defrosting using a vehicle's air conditioning systems.
Due to the limitations inherent to these systems and methods, systems for vibrating of windows by means of ultra sonic waves transducers were introduced, for hampering of ice formation. The transducer converts an electronic drive signal into mechanical vibrations, resulting in the emission of acoustic waves.
Ultrasound (i.e., acoustic waves having a frequency greater than about 20 kilohertz), is widely used in many industrial, military and medical applications. Some examples are medical diagnostics, underwater sonar imaging, cleaning, medical therapeutic, welding and bonding applications. The last three examples utilize heating effect of ultrasound. The acoustical energy of the mechanical stress waves propagating in a medium is transformed to heat due to absorption along the acoustic propagation path.
In contrast to the liquids, sound wave propagation in solids is carried out by longitudinal waves, which are also referred to as primary waves and P-waves, and secondary waves, which are also referred to as shears waves and S-waves.
In addition, thin solid sheets like glass windows act like waveguides and mix longitudinal and shear wave components and produce a variety of vibration modes.
However, it is not enough to attach an ultrasonic transducer to a window in order to prevent formation of ice and frost on a window as well as removing them based on the power sources available to such transducers on one hand and the required rate of de-icing on the other hand, for example.
In order to achieve results that will enable a substantial improvement over the existing systems' and methods' performance, for example, in de-icing the outer side of a vehicle windshield and preventing the accumulation of frost on the inner side of the windshield, thus providing safe conditions for driving within a short time from starting the car engine, the present invention suggests an optimization method which enables the selection of the ultrasonic transducers, the working frequencies, the transmission power, the locations and ways of attaching the ultrasonic transducers to the vehicle's windshield, for providing a windshield high-intensity heating system.
Such optimization is possible when specific required parameters of the vehicle's windshield are known and each parameter's influence on the system's components on the result is understood.
A window ice formation hampering apparatus is described in PCT patent application No. PCT/US2000/012915 of Lenhardt. Lenhardt describes a vehicle ice formation hampering system utilizes at least one ultrasound frequency to retard the formation of ice or frost on a window of the vehicle, which is incorporated by reference for all purposes as if fully set forth herein.
FIG. 1 of the prior art illustrates an ice formation hampering system according to the invention of Lenhardt.
Two ultrasonic transducers (or vibrators) 20 are coupled to a window of the car, for example, the front flat windshield 31.
Amongst other possibilities, the ultrasonic transducers 20 may be piezoelectric devices.
According to Lenhardt when the ultrasonic transducers 20 vibrate the flat windshield 31 hampering of ice formation is achieved.
The prior art systems and methods do provide a hampering only solution but do not provide a good solution for clearing a defrosted or deiced windshield and do not provide a solution to the need for adjusting the system to varying parameters of different kinds of vehicle windshields.
There is therefore a need for a system for deicing and defrosting, that will improve the known performances and that would fit best for varying types of vehicle windshields.